LONDON — Hoping to quell controversy after large swaths of seats appeared unfilled, London Olympic organizers said British troops and schoolchildren had been given free tickets Sunday to fill many of the vacant rows.

A day after the city reveled in the splendor of Danny Boyle’s critically acclaimed Opening Ceremonies, many locals were piqued Saturday when television footage showed empty seats at some of the most popular sporting events, including swimming and gymnastics, that they had been told were sold out. Such scenes ignited speculation that corporate sponsors had been provided tickets they weren’t using, leaving the public on the outside looking in.

Culture Secretary Jeremy Hunt, the minister responsible for the Olympics, said Saturday that the organizing committee was “doing a full investigation into what happened. . . .We think it was accredited seats that belong to sponsors, but if they are not going to turn up, we want those tickets to be available for members of the public, because that creates the best atmosphere.”

The International Olympic Committee moved quickly to quash those rumors, saying sponsors had been allocated about 8 percent of available tickets, while at the same time they tried to determine exactly whom the unused seats belonged to.

At a briefing at the Olympic Park, IOC Communications Director Mark Adams said blame for the no-shows was widespread.

“There are a range of people, four or five different groups,” Adams said, “ranging, as you heard, from the federations, the actual sports organizations involved, athletes as well, some media tickets there as well, by the way, and actually I would say it is about a handful of sponsors.”

Several sponsors, including Coca-Cola, Visa and McDonald’s, issued statements Sunday denying they had failed to use their allocated tickets.

“I think it is wrong — completely wrong — to say this is a sponsor issue,” Adams said.

Ticketing has been a particularly touchy issue here. Hundreds of thousands failed to secure seats for the events they wanted following a complicated lottery process.

Officials said they have sold more than 7 million tickets — more than were sold at the Beijing Games in 2008 — and unticketed events such as the 155-mile men’s cycling road race Saturday attracted more than 1 million spectators who lined a route stretching from outside Buckingham Palace to the English countryside.

On Sunday, many venues appeared full, but there were reports of empty seats at the Basketball Arena, where the U.S. men beat France, and Greenwich Park, where Zara Phillips, the queen’s granddaughter, was competing in equestrian.

On a rainy day at Wimbledon, Doreen Beeton stood on Henman Hill lamenting the half-filled Centre Court she saw on a giant video scoreboard. She believes many sponsors who were provided with tickets have no interest in the early-round matches.

“They won’t let us in to fill them,” Beeton said, shaking her head.

Scrambling to calm the furor, London 2012 chairman Sebastian Coe said off-duty military and students already accredited for the Olympic Park would be offered the abandoned seats. British troops already were attending women’s gymnastics Sunday morning, Coe said.

“There are a whole bunch of the military actually sitting in those seats at the moment,” he said. “And we can and we have moved them in there. And we can do that because you are not actually impacting on the operational integrity of those venues and security.”

Coe also insisted the large majority of venues were brimming with fans, and that the issue would disappear after the preliminary rounds when interest would grow.

This isn’t the first time organizers have come under fire for ticketing mishaps. Earlier this month, they withdrew 500,000 tickets for soccer matches following meager demand in large stadiums dotted around the country. They also announced in July they were offering refunds to thousands of ticket holders in the 10-meter platform diving event because the position of their seats meant that the divers would briefly jump out of view.

Following the embarrassing images of unfilled seats, a resale system was introduced over the weekend whereby people leaving an event early can return tickets that can later be sold to people already in the Olympic Park. On Saturday, nearly 300 tickets for handball were recycled this way.

Organizers also said they would try to sell unused tickets to the public. On Saturday night, nearly 1,000 tickets for gymnastics previously earmarked for the “Olympic family” were put on sale to the public. They were immediately snapped up.

Faisal Lalani, 48, who had tried and failed last year to get tickets for swimming, came to the Olympic Park on Sunday hoping to snag one of the unused tickets he read about.

Standing outside of the entrance to the Olympic Park, with grandiose views of the Aquatics Centre and Orbit tower, he said, “I feel cheated.”

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